Berendsen Thermostat and Barostat

Dear Lammps users,

I am trying to simulate quenching a system from 2000 K to 50 K (at large rates of 1e13-1e12 K/s) using Berensen thermostat and barostat. As there was a considerable initial temperature rise, I tried wide range of Pdamp and Tdamp. With all of these parameter, the very unrealistic result I got is that the volume of the system increases significantly with temperature decrease. The first question of mine is how this is possible and how I can solve this issue? ( I am trying to repeat some other group’s work in which they used Berendsen thermostat, therefore I am interested in this thermostat). It may be necessary to add that the results of potential energy is far away from the same simulation using Nose-Hover thermostat/barostat, although the pressure is kept less fluctuating around the desirable pressure, zero.

As I went through the mailing list archive, I found a suggestion to use Berendsen thermostat along fix nph (for keeping pressure constant). The second question of mine raised here as if this represents the same NPT ensemble? I am not sure how this works! Do you suggest this?

Best regards,

Muhammad

Dear Lammps users,

I am trying to simulate quenching a system from 2000 K to 50 K (at large rates of 1e13-1e12 K/s) using Berensen thermostat and barostat. As there was a considerable initial temperature rise, I tried wide range of Pdamp and Tdamp. With all of these parameter, the very unrealistic result I got is that the volume of the system increases significantly with temperature decrease. The first question of mine is how this is possible and how I can solve this issue? ( I am trying to repeat some other group’s work in which they used Berendsen thermostat, therefore I am interested in this thermostat). It may be necessary to add that the results of potential energy is far away from the same simulation using Nose-Hover thermostat/barostat, although the pressure is kept less fluctuating around the desirable pressure, zero.

As I went through the mailing list archive, I found a suggestion to use Berendsen thermostat along fix nph (for keeping pressure constant). The second question of mine raised here as if this represents the same NPT ensemble? I am not sure how this works! Do you suggest this?

Best regards,

Muhammad

2015-02-02 13:36 GMT+01:00 Muhammad R Hassani <[email protected]>:

Dear Lammps users,

I am trying to simulate quenching a system from 2000 K to 50 K (at large
rates of 1e13-1e12 K/s) using Berensen thermostat and barostat. As there
was a considerable initial temperature rise, I tried wide range of Pdamp
and Tdamp. With all of these parameter, the very unrealistic result I got
is that the volume of the system increases significantly with temperature
decrease. The first question of mine is how this is possible and how I can
solve this issue? ( I am trying to repeat some other group's work in which
they used Berendsen thermostat, therefore I am interested in this
thermostat). It may be necessary to add that the results of potential
energy is far away from the same simulation using Nose-Hover
thermostat/barostat, although the pressure is kept less fluctuating around
the desirable pressure, zero.

Was the system you start with, the one at 2000 K, well-equilibrated at that
temperature/pressure?

Kristof

Dear Kristof,

Thanks for your response. yes, I equilibrated the system at 2000K for 2ns using the same thermostat and barostat. The results for temperature, potential energy and volume in equilibration process were the same as the simulations with Nose-Hover thermostat.

Best regards
Muhammad

Dear Lammps users,

I am trying to simulate quenching a system from 2000 K to 50 K (at large
rates of 1e13-1e12 K/s) using Berensen thermostat and barostat. As there
was a considerable initial temperature rise, I tried wide range of Pdamp and
Tdamp. With all of these parameter, the very unrealistic result I got is
that the volume of the system increases significantly with temperature
decrease. The first question of mine is how this is possible and how I can
solve this issue? ( I am trying to repeat some other group's work in which

this sounds as if there is something wrong with your force field
settings or something else in your input. i doubt that it will be due
to the thermostat or barostat, if the system was properly
equilibrated.

they used Berendsen thermostat, therefore I am interested in this
thermostat). It may be necessary to add that the results of potential energy
is far away from the same simulation using Nose-Hover thermostat/barostat,
although the pressure is kept less fluctuating around the desirable
pressure, zero.

a nose-hoover thermostat is by construction not able transfer large
amounts of kinetic energy quickly.

As I went through the mailing list archive, I found a suggestion to use
Berendsen thermostat along fix nph (for keeping pressure constant). The
second question of mine raised here as if this represents the same NPT
ensemble? I am not sure how this works! Do you suggest this?

a berendsen thermostat or barostat does not in any form recreate a
standard statistical mechanical ensemble. these concepts make not much
sense in non-equilibrium settings as yours, anyway.

axel.